carusowi... while I see where you're coming from, I'm not just "repeating what I've read or heard" here. I've handled both of those cameras, among many SLRs and other cameras of various types over the years. I currently own neither a Nikon nor a Sony system (though I previously used the Minolta Dynax 35mm system), so I have nothing to prove there. My post was not meant as a criticism of Sony but actually a defence.
It's good that you decided the Sony meets your needs despite it "not being pro-level". All that really matters about equipment is whether it meets your needs. For you, for me, and for the vast majority of folks, that does not mean a product designed for professionals, so why should it not being "pro-level" even enter into it?
That said, it should be acknowledged that cameras are built to different standards, with different materials, some being more advanced mechanically and/or electronically... and with price tags to match. The D200 for example (which according to Nikon's own literature the D200 isn't a professional camera anyway!) is not only metal-bodied but also weather-sealed. Now not everybody needs a stronger body or weather-sealing. Not everyone needs a particular metering system, a particularly high shutter speed, or for certain settings to be more adjustable. People have different priorities... in your case if you have Minolta lenses, obviously Sony is going to be the first choice, and if weight is an issue then clearly a lighter camera like the A100 is better. That doesn't mean there aren't advantages to more expensive products; it just means they aren't important to you.
To give an example, I used to use a Minolta Dynax 5... what I would consider the 35mm equivalent of the A100. But when I had the chance to get a Dynax 7 at a good price, I took it... the 7 not only had better spec in terms of shutter speed and continuous shooting... it was also IMO a much better design in that it placed every control you could possibly want on a separate dial or button, so controlling the focus and exposure was more quick and convenient. Its larger size also just felt more comfortable and provided for better balance, even if it was at the expense of being heavier... those were the things that mattered to me, not what "level" someone called it...
Now in theory I could have spent a lot more and got a Dynax 9. The 9 being yet more solid, having even higher "spec", in general being what some would consider "pro-level"... but I didn't need that. The advantages didn't outweigh the costs. Using a Dynax 7 didn't make me a better photographer than using a 5, but I felt it made my life easier. On the other hand I didn't need or want a 9... but other people did and paid the difference... that didn't bother me - why should it?
All of which is just my incredibly long way of saying... use what's most suitable and reliable for you, because that's all that really matters, not what someone else uses or says.